initrd_size_decrease: remove mlxsw_spectrum/mlxsw_core kernel modules

This commit is part of the effort to decrease the initrd size:
Partially-Fixes: flatcar/Flatcar#1381

Signed-off-by: Adrian Vladu <avladu@cloudbasesolutions.com>

sdk_container/src/third_party/coreos-overlay/sys-kernel/coreos-modules/files/amd64_defconfig-6.6

@@ -81,8 +81,6 @@ CONFIG_MEMORY_HOTPLUG=y
 CONFIG_MEMORY_HOTREMOVE=y
 CONFIG_MEM_SOFT_DIRTY=y
 CONFIG_MICROSOFT_MANA=m
-CONFIG_MLXSW_CORE=m
-CONFIG_MLXSW_SPECTRUM=m
 CONFIG_MMC_SDHCI_ACPI=m
 # CONFIG_MOUSE_PS2_LIFEBOOK is not set
 CONFIG_MTRR_SANITIZER_ENABLE_DEFAULT=1